This process is particularly advantageous to perform the procedure of starting engines wherein the engine automatic switching-off is provided when the vehicle is still, and preferably it suits to single-cylinder motors for motor vehicles such as scooters and the like, wherein the electric motor, which obviously even acts as generator, is fitted directly on the driveshaft.
In this configuration, one tries to optimize the sizes and the torque which the electric motor has to exert to be able to carry out the functions thereof.
To this purpose, when the motor has to be re-started, that is when the motor switches off as the vehicle has stopped, a re-starting procedure is used providing the rotation of the electric motor to arrange the piston, inside the cylinder, in the position requesting the lowest possible torque for re-starting, by considering that the latter has to take place during a very short instant, by absolutely avoiding the stall of the piston inside the cylinder.
The U.S. Pat. No. 5,458,098 A describes a procedure of this type, devised for multi-cylinder motors of automobile type.
Generally, the electric motor in this phase is rotated with a limited torque therefore the piston cannot exceed the upper dead centre corresponding to the compression phase, by rotating the driveshaft both forwards and backwards.
In the above-mentioned document, upon each stop a backward rotation is performed, said inverse rotation to move away the pistons from the closest compression phase: from this point on the electric motor is rotated forwards for the starting, the kinetic energy which is accumulated during the forward rotation allows exceeding the closest compression phase by re-starting the engine, even if the torque would not have been sufficient to exceed it by starting from a much more approached phase.
The inverse rotation is performed by a pre-established rotation angle (π/4 in case of an engine with four cylinders wherein there is a compression phase every π/2 of rotation) or for a pre-established rotation time, provided that the piston does not prevent the inverse rotation before.
However, in a single-cylinder engine, the adjacent compression phases are spaced apart therebetween, in terms of rotation angle by an angle of 2π, and therefore, it is difficult to establish a fixed angle and/or inverse rotation time to be sure to perform the re-starting.
Even in the U.S. Pat. No. 5,713,320 A a procedure similar to the previous one is described, wherein the electric motor is rotated inversely with low power, until reaching the closest compression phase.
The European patent Nr. 1,046,813 describes an inverse rotation procedure, wherein the intervention of a sensor is provided, detecting the friction during it, to understand when the inverse rotation can cease.
However, it is to be noted that this kind of sensor has to be forcedly an additional component of the switching-on system, and an extra resource to be managed.
On the contrary, the European patent Nr. 1,233,175 describes a procedure using a sensor able to detect the absolute angular position of the driveshaft, therefor the comment of the previous document is valid.
Analogously, the European patent Nr. 1,321,666 still describes a procedure wherein the inverse rotation angle applied to the crankshaft is detected.
The procedure of the European patent application Nr. 1,365,145 is analogous to those described in the mentioned documents.
In the procedure of the European patent Nr. 1,375,907, in order to understand when the inverse rotation has to be interrupted, the speed of the crankshaft, instead of the position thereof, is detected, thus by requesting the presence of an additional sensor.
On the contrary, the U.S. Pat. No. 6,877,470 describes a procedure wherein the inverse rotation is preceded by a forward rotation until the compression phase, indeed to be able to use a finished quantity of inverse rotation. However, this procedure is devised for the automobile field wherein small rotations and high torques are involved.
The European patent application Nr. 1,055,816 A1 describes a procedure wherein the positioning has to be made by knowing the engine angular position with high precision, in order to be able to perform a re-starting.
The technical problem underlying the present invention consists in providing a switching-on process allowing to obviate the drawbacks mentioned with reference to the known art.